Test procedure for determination of air drag of heavy duty vehichles

Project duration: 2010 - 2016

Funded by: EU (DG GROW, DG CLIMA)

Project team: M. Rexeis, M. Dippold, A. Kies

Since 2010 the Institute has a leading role in the development of a European certification procedure for CO2 emissions of Heavy Duty Vehicles (HDV). The procedure is based on measurement of energy demand or energy efficiency of the single vehicle components and simulation of fuel consumption and CO2-Emissions using the software „VECTO“ (Vehicle Energy Consumption Calculation Tool).

Air drag is a key influencing parameter on the CO2 emissions of HDV, especially for vehicles operated in long-haul and regional operation. Within the framework of the EU-wide CO2 certification a new measurement method for the air drag was developed in close collaboration of the Institute with vehicle industry. The basic principle of the method - the so-called "Constant Speed Test" - is the measurement of the sum of the driving resistances by torque measurement on the driven axle as well as the vehicle inflow (air speed and angle) by means of an anemometer mounted on the vehicle. In the test procedure, measurements are carried out at 15 km/h as well as at 90 km/h vehicle speed following a precisely prescribed procedure for calibrating the measured quantities and conditioning the tire temperatures.

Air drag measurements based on the „Constant Speed Test“

Then air resistance is isolated from rolling and gradient resistance using mathematical methods and the crosswind influence on the test result is corrected. For this data evaluation the “VECTO Air Drag” software was developed at the Institute. The use of this tool is mandatory for the determination of the CdxA value in the framework of the CO2 certification.

Schematic picture of the data evaluation using VECTO Air Drag

Schematic picture of the data evaluation using VECTO Air Drag

In the final phase of the process development, additional aspects essential for the applicability and robustness of the method as part of a certification process have been elaborated. These include:

  • Accuracy requirements and calibration procedures for the measuring systems used,
  • Definition of standard superstructures and standard trailers which have to be used on the trucks or with tractors during the test procedure,
  • "family concept" rules which determine which vehicle configurations from cabin shapes, roof, chassis, etc., can be assigned to a measured CdxA value in order to limit the number of necessary vehicle measurements,
  • Rules for "Conformity of Production" measurements which are obligatory to verify the CdxA value declared by the OEM value on a sample of production vehicles.

A legal text describing the entire process was drafted within the framework of working groups with representatives from the industry, NGOs and the Commission under the direction of the Institute. The provisions are expected to be decided in the course of Q4 2016.